I've narrowed the issue down to the "contract_inner.Id = contract_outer.Id" restriction. Maybe it is having trouble traversing up through two layers of subqueries?

I am using NHibernate 2.1 btw.

I seem to be the only person getting this exception - if you google for the exception message another one of my Stackoverflow posts comes up number one. This question is similar, but different. So frustrating!